A man sits in the water in a flooded slum as floods advance into central Bangkok. Floodwater swamped a new area of Thailand's capital on Wednesday as some shops started rationing food and the prime minister warned that parts of Bangkok could be flooded for up to a month.

Damir Sagolj/Reuters

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Bangkok

As the most severe flooding to hit Thailand in decades began to enter the heart of Bangkok's temple-dotted, tourist-magnet riverside districts today, Thailand's authorities conceded that there is a high possibility that most of the city's sprawling population of some 12 million could be inundated.

On Tuesday night, Thailand Prime Minister Yingluck Shinawatra broke from earlier assurances that Bangkok could be safe from flooding and announced that "The power of the water is more than the flood barriers and water gates can withstand." She added that “There is a high possibility that water will break into inner and central Bangkok as well as outlying areas."

While most of the city – which satellite images show to be surrounded by a mass of water – remains dry, the rush of water over river barriers today was a reminder of the precarious situation now facing Bangkok, where drinking water, nonperishable foods, and water purification tablets are running low, and threaten to disrupt Thailand's economic zone and tourism industry.

“Now, everything depends on the river, and how high it might get,” says Anurak Praeroj, standing knee deep in fast running water and watching his staff line sandbags in front of his boarded up art gallery and cafe in an attempt to stem the flow coming from the river 30 yards behind.

Overflow from the Chao Praya river, which snakes through the city, washed into neighborhoods on both Wednesday, threatening the hospital grounds on one side of the river where 84-year-old King Bhumibol Adulyadej is currently staying. Across the river, the famous Grand Palace and Emerald Buddha are both also threatened. Ankle-deep water lapped at the gates of the Grand Palace by dusk on Wednesday. Farther inside the the city, some government buildings in the Lak Si district were reportedly seeing about 4 inches of water sloshing around their parking lots. Experts say water levels in Bangkok could reach as high as 5 feet if dikes to the north of the capital break.

Earlier today, on the east side of the river and a 10-minute walk from the Emerald Buddha, the famous businesses in backpacker mecca Khao San Road seemed to be taking a more complacent view of the nearby rising waters. Unlike much of the rest of the city, including the finance district inland, most shops and bars had not laid sandbag barriers by Wednesday afternoon.

Uthai Thaisagate manages the Central Digital Lab, a camera shop on that Khao San strip. He says, “80 percent of customers are gone.” He adds that he sees it as a reflection of reduced tourist numbers, as visitors are deterred by the looming inundation.

Still, flip-flop- and vest-wearing young backpackers ambled outside, perhaps safe in the knowledge that they could fly or take a bus to Thailand's southern resort islands and beaches, far from the Connecticut-sized flood zone closing in on Bangkok.

Many locals appear to be thinking along similar lines, and large numbers of Bangkok residents were evacuating to nearby cities such as Pattaya and Hua Hin, with domestic flights selling out fast after one of Bangkok's domestic airports – now site of the government's temporary flood management agency – was closed on Tuesday.

The Thailand government has declared a public holiday from tomorrow through to next Tuesday, to encourage those who need to flee or to bolster home defenses and supplies. Some 366 people are reported dead from the disaster, which has submerged provinces to the north of the capital and is likely to shave 1 to 2 percent off GDP growth in 2011.

Precise information about the flood has been hard to come by, however, generating public anger, as the Thailand government and the Bangkok Metropolitan Authority have been at odds in public. Earlier Wednesday the BMA downgraded an evacuation recommendation for riverside residents, rather saying that they need to be cautious. But as city landmarks see their first floodwaters, concerns are growing for the city's flood defenses.

“We have about 3.5 meter [11.5 feet] high dyke on the Hok Wa canal,” says Bhichit Rattakul, executive director of the Asian Disaster Preparedness Center, speaking Wednesday evening. “This is the last defense.”